The present invention relates to a liquid distributor tray for a distillation column in which a descending liquid phase of a mixture to be separated is collected and redistributed between beds of packing elements. More particularly, the present invention relates to such a liquid distributor tray in which rows of elongated liquid collectors are located above rows of vapor risers and between rows of apertures located within the distributor tray for collecting part of the liquid descending within the column and then directing/channeling such liquid to a central region of the tray.
It is well known to separate mixtures within distillation columns by a process known as fractional distillation. In accordance with such method, ascending vapor and descending liquid phases of a mixture to be separated are formed within a column. The ascending vapor phase becomes richer in the light components of the mixture as it ascends and the descending liquid phase becomes richer in the heavier components of the mixture as it descends due to mass transfer between the phases. In order to carry out the process the vapor and liquid phases are contacted by mass transfer media such as random or structured packings. Packings are contained within the column in discrete regions known as beds. Liquid is distributed onto the top/upper surface of the beds and the packing causes the liquid to spread out such that a descending film of the liquid is formed. The vapor phase rises through the packing elements and contacts the liquid phase to effect the required mass transfer.
The efficiency of such packing depends upon the degree to which liquid mixes with vapor as well as adjacent liquid within the packing bed. However, in forming the film, the liquid tends to spread out randomly across the cross-section of the column. In order to foster uniform liquid mixing, liquid is redistributed between beds of packing. This redistribution is effected by known liquid distributor trays that are designed to collect the liquid and then to distribute the collected liquid through a regular arrangement of apertures such as holes in the tray or metering tubes spaced at regular intervals. In order to allow vapor to pass upwardly through the tray without substantial pressure drop, vapor risers, also known in the art as chimneys, are connected to the tray in a regular arrangement between the apertures.
In order to promote liquid mixing in the distributor tray, various devices are employed to collect and centrally distribute descending liquid onto the distributor tray. For instance, chevron-like collector vanes are positioned to catch all descending liquid before such liquid reaches the distributor tray. The chevron-like collector vanes are provided with openings at opposite ends thereof to distribute liquid to a ring channel located above the distributor tray. The ring channel is an annular device having a central open area. Liquid overflows the ring channel and falls through the central open area onto the distributor tray. Alternatively, a collector tray arrangement is employed in which collector trays are positioned above the distributor tray. The collector tray has a central open area from which liquid flows to the distributor tray. Central distributor troughs connected and thus supported by vapor risers are employed to redistribute liquid onto the distributor tray for greater mixing of the descending liquid.
As can be appreciated, the use of a ring channel or a collector tray, in addition to the liquid distributor tray, adds to the expense and complexity of the column Additionally, in order to prevent maldistribution of the liquid due to imperfections in the surface of the tray, liquid distributor trays can be fabricated by welded, stainless steel construction. Welding in and of itself can produce local deformation and distortion. This is prevented by employing relatively thick stock in the fabrication of liquid distributor trays. As a result, liquid distributor trays are often heavy, expensive fixtures.
As will be discussed, the present invention provides a liquid distributor tray that is designed to promote liquid mixing between beds of packing without the use of separate appliances. Additionally, the present invention incorporates such object in a liquid distributor tray design that can be inexpensively and more lightly constructed than prior art liquid distributor trays.